Discontinous reception (DRX) is a method used in communication networks to conserve battery energy of receiving devices, e.g., mobile devices or user equipment (UE). The UE and the network negotiate phases in which data transfer happens. During other times the device turns its receiver off and enters into a low-power state.
One major aspect affecting the UE stand-by time is the possibility to inactivate the UE receiver circuitry. In the Universal Mobile Telecommunications System (UMTS) Radio Access Network (UTRAN), this is mainly utilized in paging states, where the UE is listening periodically to the paging channel. DRX period(s) and triggers/timers which result in DRX are typically configured by Radio Resource Control (RRC) functionality. Alternatively, the network may direct inactive UEs to DRX by explicit commands. Configuring long DRX periods allows for long standby times with the expense of elevated wake-up times for network-initiated data transfers.
Consequently, DRX has direct impact on how often the network is able to address the UE. The need for the network to be able reach/address a UE depends on the connection type(s) between the UE and network. In case of a streaming connection, the DRX cycle will most probably be different than in case of a mail download. This is linked to the quality of service (QoS) of the connection.
As UE power consumption greatly depends on how often UE has to turn on its transceiver, it is clear from the above description that the DRX interval has impact on UE power consumption. This means that one key to power saving is to make it possible to optimize the use of DRX in such a way that the network always can utilize the longest possible DRX taking the connection restrictions into account.
It is assumed that all resources are assigned more or less temporarily by the network to the UE by use of allocation tables (AT) or more general by use of a downlink (DL) resource assignment channel. These assignments or allocations may be grouped into one-time allocations and persistent allocations. One time resource assignment means that through the AT the UE will receive uplink (UL) and/or DL resource allocations which are valid only once and for that particular allocation in time. Alternatively, UL/DL resources may be assigned temporarily for a longer time period—so-called persistent allocations. This longer resource assignment may be done for longer pre-determined time or until new DRX and/or Discontinuous Transmission (DTX) information is signaled to the UE.
FIG. 2 shows time diagrams with examples of allocation schemes for one-time allocation and persistent allocation. As indicated in the upper part of FIG. 2, different filling patterns of the initial sub-frame of each DRX cycle represent different bit patterns of this initial sub-frame which may have a length of e.g., 0.5 ms. The different bit patterns are used to indicate whether an AT including UL/DL resource assignment (i.e., data reception) is provided, whether an AT not including any UUDL resource assignment (i.e., no data reception) is provided, or whether reception without any AT is intended.
In the lower part of FIG. 2, two allocation examples are shown. The upper one relates to a one-time allocation and the lower one relates to a persistent allocation. As indicated by the filling pattern of the sub-frames of the one-time allocation example, the resource allocation is only valid for one DRX cycle and each sub-frame indicates that an AT with or without UL/DL resource assignment is included, i.e., data reception or no data reception is signaled, as desired. In contrast thereto, in the persistent allocation example, only the first sub-frame at the left end of the allocation pattern indicates an AT with UL/DL assignment, while the following sub-frames only indicate data reception without AT reception due to the fact that the allocation is valid for a longer DRX cycle covering several sub-frames.
At the receiving device, e.g., mobile terminal or UE, two operating modes may be provided: idle mode and active mode (also called RRC connected mode). In idle mode, mobility is based on UE-initiated or autonomous cell reselection, while in the active mode, mobility is based on UE-assisted network-commanded handover (HO). UE assistance is in this sense is achieved through delivery of measurements reports.
In this regard, a problem arises as there are so far no thoughts about how to handle the combination of having a packet switched connection with some varying (possibly long) DRX period, and thereby varying response time in DL from network to UE in situations where UE sends a measurement report.
An event triggered measurement reporting from the UE to the network may be used in order to supply the network with information required in the HO algorithm and HO decision process. Periodical reporting may also be considered at least for selected cases. The UE can send measurement reports at any time using normal access procedures, whereas the network can only reach the UE through the AT. As explained above, the UE will only receive ATs at certain points in time—determined by the DRX period. This means that there will be a delay in DL for the network before it is able to reach the UE with a possible HO command, wherein the delay depends on the current DRX period. The delay in the HO procedure caused by the delay in transferring the HO command to the UE may have unwanted side-effects and impact on network planning.